OK- this is likely 'intuitively obvious to even the most casual observer' (shades of school! ) - but I'm going to ask....

When you do (say, a 50%) water change:
(Assuming I've prepared treated water in gallon jugs that have also sat for 24 hrs:)
Do you take the fish out (placing in current aquarium water), then remove 50% of the water, then replace 50% water, then add back fishie(s)?

Or do you do it with them in the tank? (wouldn't that be disturbing?), or?

Also-
Do you ruffle up the gravel*, etc (to have the filter do some work) while you're changing the water (or do you need to buy a vacuum to do that)?- or do I leave it alone? (trying not to mess up bacterial functions, etc.)

(*I briefly worked at a fish store where they did so to clean the fresh water tanks on a daily basis- looked terrible for ~5 minutes but they had an integrated industrial sized (really)pump/ filter setup for the entire place that had the tanks looking pristine in 5 minutes time).

I know that water changes are as routine as toothbrushing for some, but just trying to do it correctly for my lil buddy (no industrial setup here! ha!) & am not making assumptions!

For partial water changes no need to remove the fish.....and for gravel/substrate cleaning...if you don't have a vacuum...then ruffle or stir the substrate to get the mulm/debris up in the water column to either siphon or dip out... at least weekly....50% is just an estimate....eye-ball it.....fish keeping is not an exact science and neither are water changes...lol.....lot of ways to do it that are correct...it varies from one keeper to the next.....you have to find what works best for you.....

If you have been doing water changes and cleaning the substrate on a regular basis...then the water should clear within an hour or less...if not, then you are either overfeeding, overstocked or missed a water change....

Remember to unplug the filter and heater before water changes and remember to plug everything back in once you re-fill.....

Remember to always use dechlorinater with any water added to the fish/tank if on city water supply

Remember to keep the water temp within a couple of degrees between new and old water with water changes....

Remember to wash your hands before and after working with the aquarium/fish

Remember-the good bacteria for the nitrogen cycle are sticking and adhere to everything inside the tank, in the top layer of substrate and in the filter media....very little are in the water column so water changes should not affect the nitrogen cycle, however, over cleaning, vacuuming more than weekly, over cleaning or using chlorinated tap water on the filter media can cause mini cycle/ammonia spikes.

Remember-regardless of filtration or not-water changes are still needed on a regular basis-filters can remove debris from the water column so you can't see it but it is still in the tank...out of sight trapped in the filter media.....

Use a gravel vacuum and siphon water into a 5 gal bucket. I am always prodding the vaccuum into the gravel. Not too deep though, as my tank is planted and I dont want to disturb roots. If you don't have plants you don't have to worry about this. Usually do a 40-50% WC. I just eyeball it. Once the water level is about half of what it used to be, I stop siphoning.

Gently swish filter media in old water (in the bucket). Dont over do this though - Gently because you dont want to disturb the bacteria colony.

After that, I use a jug and use HOT water from the tap and mix it in the bucket until desired temp is reached (because hose water is cold).

Add dechlorinator

Use a gallon jug to carefully pour new water into the tank. I pour it over my driftwood as to not disturb my gravel/ fish/ live plants/ and to minimize current

Plug in electrical appliances

Whole process takes me 10-15 minutes.

A siphon isn't needed but will make life alot easier and make the process much quicker. Especially if you have a larger tank. I recommended one. You can find them at your LPS. I only paid $8 for mine. Got it at Wal-Mart.

Remember to unplug the filter and heater before water changes and remember to plug everything back in once you re-fill.....

OFL.. I unplug my heater but not my filter when i do my changes. I have a bio-wheel and it runs fine when I am doing the changes, just dribbles more and the baffle is rendered usless for the duration of time I am doing it. lol. nice little water fall effect. not enough to disturb my betta though he actually likes it and always tries to play in it and the water i am pouring back in lol